One form of flask for the transport of nuclear fuel comprises a vessel having a removable closure member at one end. The flask accommodates a bottle or magazine containing the fuel and the flask is emptied by setting in an upright position with the removable closure member at its lower end whereby upon removal of the closure member the bottle or magazine can be lowered out of the flask. As the fuel within the bottle or magazine is submerged in water which can leak out of the bottle it is necessary as a safety feature to ensure that the end closure member effect a liquid tight seal at the end of the flask.
It has been proposed to utilise a wedge-shaped member to effect a seal whereby lateral movement of the wedge-shaped member across the end of the flask causes an initial vertical displacement of the end closure member to break the seal at the end of the flask. This has the advantage of reducing damage to the seal by a tearing action which could arise if the closure member was moved laterally across the end of the flask seal face without any initial separation. However the use of a single wedge-shaped member results in an end closure member of a non-uniform thickness.